Modern selective call systems are rapidly evolving into two-way radio messaging systems. Two-way systems advantageously provide confirmation of message delivery, as well as automatic retry upon a failure of a message delivery attempt. In addition, two-way systems allow users of portable subscriber units to originate as well as receive messages.
A problem with a two-way radio messaging system is that the transmitter power of the portable subscriber unit, and thus the transmission range, is limited by battery life considerations. As a result, multiple, high sensitivity base receivers usually are distributed about the system to achieve good reliability of inbound (i.e., portable subscriber unit to base receiver) transmissions. Such base receivers undesirably add cost to the infrastructure of the system, and service providers understandably want to minimize the number required. Sometimes, especially in new systems, economic constraints result in an insufficient number of base receivers for adequate inbound coverage throughout the outbound coverage area.
Thus, what is needed is a reliable method and apparatus for inbound transmission in a two-way radio messaging system. Preferably, the method and apparatus will provide reliable inbound transmissions using fewer base receivers in the system, compared to prior art techniques.